The invention relates to a camera tube comprising an electron gun in one end of a tubular evacuated envelope. The electron gun consists of a cathode, which is placed on an axis and has an emissive surface extending substantially perpendicular to the axis, and an electrode having a central aperture in a part of the electrode which is perpendicular to the axis. The central aperture is partly closed by means of an apertured plate. The cathode is connected to a metal cathode support bush so as to be electrically insulated from the support and substantially concentric to the support. The support comprises a part which extends perpendicular to the axis and is placed against the part of the electrode extending perpendicular. The parts of the support and the electrode which extend perpendicular to the axis are connected together.
The invention also relates to a method of manufacturing such a camera tube.
Such camera tubes have a wide field of application, for example, television cameras and infrared cameras.
Such an electron gun is known from Funk Technik, No. 1--1978, pages 1-6, in which a cathode is connectedto the cathode support by means of a plug of insulating material. The cathode support is secured to a first grid (wehnelt electrode). The first grid has a central circular aperture in which the cathode support is centered by means of a coaxial groove. Such a construction is much too inaccurate for use in a television camera tube having an electron gun of the type described above. The cathode is frequently assembled in a noncentral and inclined position in the cathode support. Positioning corrections are no longer possible after the cathode is mounted in the cathode support.
A similar camera tube and in particular a similar electron gun is disclosed in U.S. Pat. No. 3,894,261. However, nothing is stated about the construction, the positioning and the connection of the cathode, cathode support and anode.
In addition to the diode gun, such tubes include a focusing lens to focus the generated electron beam on a photoconductive layer provided on a signal plate. A potential distribution is produced on the photoconductive layer by projecting an optical image on it. By scanning the photoconductive layer with the electron beam, the signal plate provides signals which correspond to the optical image. The formation of an electron beam and the scanning with the electron beam provides many problems, particularly in the case of small camera tubes. It has been found, for example, that, if the central path of the electron beam passing through the aperture in the anode plate encloses an angle of 1.degree. with the axis of the gun, the intensity of the electron beam impinging on the photoconductive layer (the beam current) is already reduced by 25%. Since it is substantially impossible, in assembling the above-described construction known from Funk Technik, No. 1, 1978, to cause the gun axis and the central path to coincide substantially, it is not attractive to use such a gun in camera tubes because the noncoincidence has to be corrected by means of extra correction coils.